Electrophoresis is a technique by which particles such as mixtures of macromolecules are moved through a gel matrix by an electric field. It is a widely used technique for quantitative analysis and for separation, recovery and purification of certain macromolecular species. It is widely used for the study of proteins, nucleic acids and chromosomes. Until recently, it has been difficult to electrophoretically separate very large particles.
Recently, pulsed-field gradient, gel electrophoretic systems have come into being which make possible the resolution of large DNA molecules. These systems, in essence, repetitively alter the field direction applied to a gel containing the DNA molecules. This alteration of the field direction produces the separation of the molecules because the molecules, depending upon their molecular weight (or contour length), vary in the amount of time required to change direction. Several different designs for employing pulsed-field techniques have been recently reported. In U.S. Pat. No. 4,473,452 to C. R. Cantor et al, a planar gel is employed which is oriented horizontally on the bottom of a buffer chamber. Several power supplies allow different voltages to be applied parallel to the plane of the gel to produce alternating fields. The design employs electrode arrays constructed from a series of vertical lengths of platinum wire in which each is isolated from the others by a diode array. Another design, described by Carle, G. F. et al, "Nucleic Acid Research", (1984), Vol. 12, No. 14, pp. 5647-5664, uses a similar structure but rather employs a continuous length of platinum wire for each electrode and avoids the use of a diode array. Though this design allows substantial short circuiting, it does perform well. Neither design, however, is able to produce gel lanes that are exposed to equivalent electrical fields and, thus, the nucleic acid samples move in a complex trajectory through the gel making subsequent interpretation somewhat difficult.
Accordingly, it is an object of this invention to provide a pulsed-field gradient, gel electrophoretic apparatus wherein all separation lanes are exposed to equivalent field strengths and orientations.
It is a further object of this invention to provide a pulsed-field gradient gel electrophoretic apparatus which provides separation lanes which are easily readable and wherein the molecules being separated follow a linear and well defined path.
It is a further object of the present invention to provide for a novel and improved electrophoretic apparatus which achieves increased resolution of the molecules within each separation lane; and further wherein the apparatus is so constructed and arranged as to be interchangeable for use in the separation and transfer of molecules from their separation lanes.